Modern surgical techniques which are relatively non-invasive have been recently developed for viewing and performing different medical procedures to the interior structure of body parts. Medical instruments for carrying out these procedures are known generally as endoscopes and specifically include arthroscopes, laproscopes, spinalscopes, esophagoscopes and others. These instruments typically include a scope which is inserted into the body part to be examined. With an arthroscope, for example, the scope is connected to a camera assembly and the camera assembly in turn is connected to a video display for generating a picture of the interior structure of a joint. Consequently, the operator of the arthroscope is able to view, in real-time, the interior structure of the joint as the scope is moved within the joint. By viewing the internal structure of the joint, a diagnosis of the joint's potential maladies can be made and appropriate treatment prescribed.
In constructing medical endoscopes one requirement is that the scope of the endoscope be relatively small. A small sized scope helps to reduce the size of an entry site into the body (i.e. joint) and also helps to minimize trauma within the body by insertion of the scope.
Coincident with the requirement of a small size, is the requirement that the probe provide as large a field of view as possible within the body. If the scope can be constructed to provide a large field of view within the body, then movement of the scope within the body can be minimized and trauma reduced accordingly.
For this reason endoscopes are often constructed with a scope adapted to provide a wide angle field of view. As an example, this may be accomplished using a viewing lens at a distal end of the scope that possesses a relatively large numerical aperture (N.A.). In addition, some scopes may be constructed with a viewing axis that is angled or oblique with respect to a longitudinal axis of the scope. This angle may be preset (i.e. 30.degree., 70.degree. and 90.degree.) to facilitate viewing of a particular body structure (i.e. knee, shoulder). With an offset viewing axis, the scope can be rotated within the joint to sweep a field of view.
In order to provide such an offset viewing axis, some endoscopes are constructed with a scope assembly having an arrangement of lens and prisms. U.S. Pat. No. 4,138,192 to Yamasita for instance, discloses such a scope assembly having an optical system that is constructed with an oblique viewing axis.
In general, the construction of this type of endoscope is relatively complicated and expensive. In addition, the scope assembly of such an endoscope may be relatively large or difficult to move within the body. Moreover, because of the expense of the scope assembly, the scope assembly must be reused and sterilized after each use. In view of the possibility of disease transmission between patients, endoscopes that utilize a disposable scope assembly have been introduced in recent years. In general, these disposable scopes are safer and easier to use than endoscopes having a scope assembly that must be sterilized after each use.
There is then a need in the medical field for a relatively inexpensive scope assembly for endoscopes that can provide a large field of view within the body. Further there is a need for such a scope assembly for endoscopes that is of a relatively simple construction that is disposable after a single use.
Accordingly it is an object of the present invention to provide an endoscope scope assembly that provides a full hemispherically shaped field of view within the body. It is another object of the present invention to provide such an endoscope scope assembly having a relatively small distal end for insertion into the body such that trauma to the body is minimized. It is a further object of the present invention to provide such an endoscope scope assembly that is disposable. It is a further object of the present invention to provide a scope assembly for such an endoscope that is relatively inexpensive to manufacture and easy to use yet provides an increased field of view within the body with an acceptable image quality.